How Perfect a Gluon Plasma Can Be in Perturbative QCD?

Understand

The shear viscosity to entropy density ratio, \eta /s, characterizes how perfect a fluid is.

• We calculate the leading order \eta /s of a gluon plasma in perturbation using the kinetic theory.
• The leading order contribution only involves the elastic gg -> gg (22) process and the inelastic gg<->ggg (23) process.
• The Hard-Thermal-Loop (HTL) treatment is used for the 22 matrix element, while the exact matrix element in vacuum is supplemented by the gluon Debye mass insertion for the 23 process.